This invention relates to a method of controlling a refrigeration cycle applied in, for example, an air conditioner and, more particularly, to a method of controlling the opening degree of an expansion valve built in the refrigeration cycle.
A refrigeration cycle used with, for example, an air conditioner is generally constructed by connecting a compressor, 4-way valve, outdoor-side heat exchanger, decompression unit and indoor-side heat exchanger in the order mentioned. With this type of refrigeration cycle, a coolant, sent from the compressor while being held at a high temperature and a high pressure when cooling a room, flows into the outdoor-side heat exchanger through the 4-way valve and then condenses. After being decompressed in the decompression unit, the coolant is evaporated in the indoor-side heat exchanger and brought back to the compressor. When the room is heated, the operation of the 4-way valve is changed over, causing the coolant to flow in a cycle opposite to the room-cooling cycle. Namely, when heating a room, a high temperature and a high pressure coolant sent from the compressor is first condensed in the indoor heat exchanger and then decompressed by the decompression unit. After evaporation in the outdoor heat exchanger, the coolant is returned to the compressor.
Recently, an electromotive expansion valve has been applied as a decompression unit. The opening degree of this expansion valve is controlled to regulate the operation of the refrigeration cycle.
The adjustment of the opening degree of this electromotive expansion valve controls the temperature of a coolant ejected from the compressor. If, however, the refrigeration cycle is subjected to a tremendously heavy load with respect to a particular opening degree of the expansion valve, a sharp rise takes place in the temperature at which the coolant is ejected from the compressor. This event leads to a decline in the insulation of the winding of the compressor motor, or the property of a lubrication oil held in the compressor and, consequently, in the reliability of a refrigeration cycle.